A number of organic compounds may be found in water, particularly water contaminated by various industrial processes. It is desirable to remove such compounds from the water for a large variety of reasons, ranging from water purification to recovery of the organic compounds.
As is well known to those skilled in the art, it is possible to remove water from mixtures thereof with organic liquids by various techniques including adsorption or distillation. These conventional processes, particularly distillation, are however, characterized by high capital cost. In the case of distillation, for example, the process requires expensive distillation towers, heaters, heat exchangers (reboilers, condensers, etc), together with a substantial amount of auxiliary equipment typified by pumps, collection vessels, vacuum generating equipment, etc. Such operations are characterized by high operating costs principally costs of heating and cooling-plus pumping, etc.
Furthermore, the properties of the materials being separated, as is evidenced by the distillation curves, may be such that a large number of plates may be required, etc. When the material forms an azeotrope with water, additional problems may be present which for example, would require that separation be effected in a series of steps (e.g. as in two towers) or by addition of extraneous materials to the system. There are also comparable problems which are unique to adsorption systems.
It has been found to be possible to utilize membrane systems to separate mixtures of miscible liquids by pervaporation. In this process, the charge liquid is brought into contact with a membrane film; and one component of the charge liquid preferentially permeates the membrane. The permeate is then removed as a vapor from the downstream side of the film-typically by sweeping with a carrier gas or by reducing the pressure below the saturated vapor pressure of the permeating species.
A number of pervaporation membranes have been developed for separation of azeotropes and organic compounds from water. (See Aminabhavi, T. M.; Khinnavar, R. S.; Harogoppad, S. B.; Aithal, U. S.; Nguyen, Q. T.; Hansen, K. C. J. Macromol Sci.-Rev Macromol Chem Phys 1994, C43, 139; Li, S.; Tuan, V. A.; Noble, R. D.; Falconer, J. L. Ind Eng Chem Res, 2001, 40, 4577; Yeom, C. K.; Jegal, J. G.; Lee, K. H. J Appl Polym Sci 1996, 62, 1561; Shieh, J. J.; Huang, R. Y. M. J Membrane Sci 1998, 148, 243; Okuno, H.; Uragami, T. Polymer 1992, 33, 1459.) Examples of such membranes are described in U.S. Pat. No. 2,953,502 issued on Sep. 20, 1960 to Binning, R. C. and Lee, R. J and in Neel, J.; Nguyen, Q. T.; Bruschke, H. Europaaiaches Patentamt Anmeidung 90123133.2, Dec. 21, 1990. Other pervaporation membranes include blend membranes (Chanachi, A.; Jiraratananon, R.; Uttapap, D.; Moon, G. Y.; Anderson, W. A.; Haung, R. Y. M., J Membr Sci 2000, 16, 6271; Toti, U. S.; Kariduraganavar, M. Y.; Soppimath, K. S.; Aminabhavi, T. M., J Appl Polym Sci 2002, 83, 259), composite membranes (Meier-Haack, J.; Lenk, W.; Lehmann, D.; Lunkwitz, K., J Membr Sci 2001, 184, 233; Qureshi, N.; Meagher, M. M.; Huang, J.; Hutkins, R. W., J Membr Sci 2001, 187, 93), charged membranes (Huang, S. C.; Ball, I. J.; Kaner, R. B, Macromolecules 1998, 31, 5456; Kusumocahyo, S. P.; Sudoh, M, J Membr Sci 1999, 161, 77), polyion complex membranes (Jegal, J.; Lee, K.-H., J Appl Polym Sci 1996, 60, 1177), copolymer membranes (Park, C. H.; Nam, S. Y.; Lee, Y. M.; Kujawski, W., J Membr Sci 2000, 164, 121), and grafted copolymer membranes (Ping, Z. H.; Nguyen, Q. T.; Chen, S. M.; Ding, Y. D., J Membr Sci 2002, 195, 23).
Natural polymers have also been used in pervaporation membranes. (See Okuno, H.; Uragami, T., Polymer 1992, 33, 1459; Zhang, L.; Zhou, D.; Wang, H.; Cheng, S. J Membr Sci 1997, 124, 195; Bhat, N. V.; Wavhal, D. S., J Appl Polym Sci 2000, 76, 258; Huang, R. Y. M.; Moon, G. Y.; Pal, R. J Membr Sci 2001, 184, 1; Chanachi, A.; Jiraratananon, R.; Uttapap, D.; Moon, G. Y.; Anderson, W. A.; Huang, R. Y. M. J Membr Sci 2000, 166, 271; Cao, S.; Shi, Y.; Chen, G. J Membr Sci 2000, 165, 89; Soppimath, K. S.; Aminabhavi, T. M.; Kulkarni, A. R.; Rudzinsiki, W. E. J Control Rel 2001, 70, 1; and Jiraratananon, R.; Chanachai, A.; Huang, R. Y. M.; Uttapap D. J Membr Sci 2002, 195, 143.)
Among natural polymer membranes, sodium alginate (SA) membranes are known to have superior pervaporation separation characteristics when used to separate mixtures of water and methanol or water and ethanol. (See Uragami, T.; Saito, M. Sep Sci Technol 1989, 24, 541.) Sodium alginate is a watersoluble polysaccharide that may be gelled by acid treatment or by crosslinking with glutaraldehyde or Ca ions. Sodium alginate is a coplymer composed of 1→4)-linked β-D-mannuronic acid (M) and α-L-guluronic acid (G) residues arranged in blockwise fashion.

Three different types of blocks are possible: homopolymeric MM blocks, homopolymeric GG blocks and heteropolymeric, sequentially alternating MG blocks. (See Fischer, F. G.; Dorfel, H. Hoppe Seyler's Z. Physiol Chem 1955, 302, 186; and Huang, A.; Larsan, B.; Smidsroed, O. Acta Chem Scand 1966, 20, 183.) Properties of the polymer vary based one the amount of α-L-guluronic acid (G). (See Moe, S. T.; Draget, K. I.; Break, G. S.; Smidsrod, O.; Alginates, in A. M. Stephen (Ed.), Food Polysaccharides and their Applications, First Ed., Marcel Dekker, New York, 1995, pp. 245–286.)
Mochizuki et al., studied the relationship between permselectivity of alginic acid membrane and its solid state structure as well as the effect of counter cations on membrane performance (Mochizuki, A.; Amiya, S.; Sato, Y.; Ogawara, H.; Yamashita, S. J Appl Polym Sci 1990, 40, 385). Aminabhavi et al. have prepared blend membranes of SA with polyacrylamide-grafted-gaur gum and studied their PV separation characteristics for acetic acid+water and isopropanol+water mixtures (Toti, U.S.; Kariduraganavar, M. Y.; Soppimath, K. S.; Aminabhavi, T. M. J Appl Polym Sci 2002, 83, 259; Toti, U.S.; Aminabhavi, T. M. J Appl Polym Sci 2002, Accepted). Additionally, some studies have also been carried out to understand the effect of polymer viscosity on diffusion of drugs using calcium alginate membrane coated tablets. (See Bhagat, R. H.; Mendes, R. W.; Mathiowotz, E.; Bhargava, H. N. Drug Dev Ind Pharm 1994, 20, 387; Kikuchi, A.; Kawabuchi, M.; Watanabe, A.; Sugihara, M.; Sakurai, Y.; Okano, T., J Control Rel 1999, 58, 21.)
However, sodium alginate membranes suffer from lack of mechanical stability. This problem can be corrected somewhat by cross-linking the membranes (Yeom, C. K.; Lee, K. H., J Appl Polym Sci 1998, 67, 209), blending the sodium alginate with other stable polymers (Yeom, C. K.; Lee, K. H., J Appl Polym Sci 1998, 67, 949), or by developing composite membranes (Huang, R. Y. M.; Pal, R.; Moon, G. Y. J Membr Sci. 2000, 166, 275; Kurkuri, M. D.; Toti, U.S.; Aminabhavi, T. M. J Appl Polym Sci 2002, Accepted; Yang, G.; Zhang, L.; Peng, T.; Zhong, W. J Membr Sci 2000, 175, 53). Several asymmetric membranes have been prepared as thin film composites of SA with different hydrophilic and hydrophobic support materials. (See Moon, G. Y.; Pal, R.; Huang, R. Y. M. J Membr Sci 1999, 156, 17–27; Huang, R. Y. M.; Pal, R.; Moon, G. Y. J Membr Sci 2000, 166, 275; and Wang, X. N. J Membr Sci 2000, 170, 71.) However, even sodium alginate membranes with these improvements in mechanical stability remain unsuitable for many uses.
In addition to addressing mechanical stability problems, achieving the simultaneous enhancement of both selectivity and flux or enhancement of one characteristic without decrease of the other is a challenging task in the area of pervaporation membranes. To achieve this goal, many efforts have been made to fabricate or modify different types of membranes. (See Huang, R. Y. M.; Pal, R.; Moon, G. Y. J Membrane Sci 1999, 160, 17; Jo, W. H.; Kim, H. J.; Kang, Y. S. J Appl Polym Sci 1994, 51, 529; Kim, J. H.; Lee, K. H.; Kim, S. Y. J Membrane Sci 2000, 169, 81; and Lee, K. R.; Teng, M. Y.; Lee, H. H.; Lai, J, Y. J Membrane Sci 2000, 164, 13.) For instance, efforts from different groups have utilized different types of membranes for the pervaporation separation of aqueous-organic mixtures. (See Kurkuri, M. D.; Kumbar, S. G.; Aminabhavi, T. M. J Appl Polym Sci 2002, In press; Kurkuri, M. D.; Toti, U.S.; Aminabhavi, T. M. J Appl Polym Sci 2002, In press; Toti, U. S.; Kariduraganavar, M. Y.; Soppimath, K. S.; Aminabhavi, T. M. J Appl Polym Sci 2002, 83, 259; Aminabhavi, T. M.; Naik, H. G. J Appl Polym Sci 2002, 83, 244; and Aminabhavi, T. M.; Naik, H. G. J Appl Polym Sci 2002, 83, 273.) However, improvements in flux or selectivity remain useful for improving overall pervaporation membrane quality and for allowing additional uses of such membranes.